1. Field of the Invention
The present invention relates to a train detector and a train security device of a dual gauge track circuit in which two or more types of trains having different gauges, that is, different distances between wheels, share a rail.
2. Description of the Related Art
The most important information for ensuring safety of train operation is to know where the trains are positioned within the track. Track circuits have been developed with this aim. The most popular type of track circuits is a dual rail track circuit in which closed circuits are formed via two rails. The dual rail track circuit constitutes closed circuits in which two rails are electrically separated into arbitrary sections, having transmitters for transmitting train detection signals and receivers for receiving the train detection signals transmitted from the transmitters attached to opposite ends of the sections.
The transmitters and receivers are used to monitor the reception level of train detection signals constantly so as to detect the entry of trains to the relevant section. When a train enters the relevant section between a transmitter and a receiver, the axles of the train electrically short the rails together and the reception level drops. This phenomenon of changes of the reception level is used as the mechanism for detecting entry of trains.
The prior art system devised to constitute respective track circuits for two types of trains having different gauges sharing a common rail and travelling on this dual rail track circuit is a dual gauge track circuit in which three rails are used, as shown in FIG. 8. Such prior art track circuit system is disclosed in non-patent document 1 (The Institute of Electrical Engineers of Japan, Education Investigation Commission on Electric Railways, “Latest Electric Railway Engineering”, Corona Publishing Co., Ltd, Published Sep. 11, 2000, pages 216-218).
The dual gauge track circuit shown in FIG. 8 considers performing different controls for the two types of trains having different gauges, and enables to recognize the type of the train present on the track when the presence of a train is detected. Further, the dual gauge track circuit characterizes in that induction occurs via magnetic field coupling among the three rails, and this induction effect greatly influences the transmission of electric signals supplied to the rails.
A train detector utilizing track circuits is a mechanism for detecting the presence of a train by the attenuation of train detection signals caused by the drop of rail impedance when the train enters a relevant section and shorts the rails together via its axles. In the dual gauge track circuit, mutual induction occurs among rails as mentioned earlier. The state of a track circuit when a train enters the track is as shown in FIG. 9, which is an equivalent circuit.
In FIG. 9, a train detection signal transmitted from a transmitter A 4 mainly forms a current loop of current X 8. This current X 8 generates a magnetic field X 11 around the standard track rail 1 and generates a current Y 9 via the magnetic field coupling between the standard track rail 1 and the narrow track rail 2.
Furthermore, the current Y 9 generates a magnetic field Y 12 around the narrow track rail 2 and creates a current Z 10 on the standard track rail 1, and as a result of superposing train detection signals toward the reception side, the reception level is raised and the train detection performance is deteriorated.